In the current state of the art, the electrical leadframe for an encapsulated integrated circuit comprises a central plate to which the passive face of the chip forming the integrated circuit is fixed by adhesive bonding. The connection leads are placed around the periphery of this central plate. When in particular the chip forms a power integrated circuit, it is known to couple it to a heat sink to absorb and dissipate the heat which it produces. The following solutions have been proposed to overcome difficulties with such power integrated circuits.
One known arrangement includes fixing the heat sink to that face of the central plate of the electrical leadframe on the opposite side from its face which receives the chip by adhesive bonding. In another known arrangement, the heat sink is no longer fixed by adhesive bonding but, at its four corners, has projecting studs which pass through the corners of the central plate. Those ends of the studs lying on the same side as the chip are crimped, by crushing, perpendicularly to the central plate.
In another known arrangement, the heat sink is not fixed to the electrical leadframe, but is placed in the bottom cavity of the mold into which the encapsulant is injected. The central plate of the leadframe is placed on top and in contact with it, before injecting the encapsulant, and after the mold has been closed.
Up to now, the known arrangements described above, applied to large packages, have given relatively satisfactory results with regard to dissipation of the heat produced. However, they are becoming increasingly limited from the standpoint of their capacity to dissipate the heat produced by the integrated circuit and unsuitable from a constructional and fabrication-process standpoint when it is a question of fabricating semiconductor devices in which the electronic functions are ever increasing. Moreover, the number of connections are ever increasing and may be as many as 208, and the required size of which is ever decreasing, as is the case in many electrical systems, such as microcomputers and portable telephones.